This invention relates to cementing casing in subterranean formations. In particular, this invention relates to methods for cementing a casing annulus by reverse-circulating the cement composition into the annulus without excessive cement composition entering the casing inner diameter.
It is common in the oil and gas industry to cement casing in well bores. Generally, a well bore is drilled and a casing string is inserted into the well bore. Drilling mud and/or a circulation fluid is circulated through the well bore by casing annulus and the casing inner diameter to flush excess debris from the well. As used herein, the term “circulation fluid” includes all well bore fluids typically found in a well bore prior to cementing a casing in the well bore. Cement composition is then pumped into the annulus between the casing and the well bore.
Two pumping methods have been used to place the cement composition in the annulus. In the first method, the cement composition slurry is pumped down the casing inner diameter, out through a casing shoe and/or circulation valve at the bottom of the casing and up through to annulus to its desired location. This is called a conventional-circulation direction. In the second method, the cement composition slurry is pumped directly down the annulus so as to displace well fluids present in the annulus by pushing them through the casing shoe and up into the casing inner diameter. This is called a reverse-circulation direction.
In reverse-circulation direction applications, it is sometimes not desirable for the cement composition to enter the inner diameter of the casing from the annulus through the casing shoe and/or circulation valve. This may be because, if an undesirable amount of a cement composition enters the inner diameter of the casing, once set it typically has to be drilled out before further operations are conducted in the well bore. Therefore, the drill out procedure may be avoided by preventing the cement composition from entering the inner diameter of the casing through the casing shoe and/or circulation valve.